The invention relates to electrical wiring, and optical fiber transmission structures, represented by wiring harnesses, and fiber-optic networks and the like, which include transition sections produced by diverting signal carriers from a multi-wire or multi-fiber cable into connecting branches required by the signal carrier network design. More particularly the present invention provides a protective, sealing, cable transition cover including stress-relief to accommodate repeated flexing and related distortion of branched-signal carrier transition sections during manufacture and installation of signal and electrical power carrying structures.
The development of grids for electrical power distribution and communications networks relies upon cable-based signal and power carriers that reside inside protective jackets, isolated from deleterious environments. Protective outer jacket materials for conventional cables typically exhibit low surface energy. Suitable jacket polymers include, by way of example, polyethylene, polypropylene, or copolymers or blends thereof. A low surface energy outer jacket represents a barrier to contact of signal carriers with damaging components in an external environment that could compromise the function of the signal carrying elements.
A current carrying wire or a signal carrying optical fiber may become exposed to the environment in several different ways. In one common situation a cable, containing multiple signal carriers, may be damaged by abrasive wear, which progresses through a cable cover until signal carriers become exposed. A second situation, causing signal carrier exposure, is the linking of cables and joining of signal carriers during the construction of electricity distribution grids or communications networks. This construction activity produces multiple spliced cable sections that require application of protective covers to replace the cable jacket and re-seal the signal and power carriers from the environment. Without suitable protection, cable operation and life expectancy may be adversely affected.
A variety of closures exist for protecting cables that include either spliced sections or worn portions showing evidence of jacket deterioration. Closures take the form of covers or housings for placing over portions of a cable in locations of exposed signal or power carrier elements. A closure, placed around a spliced or worn section of a cable, may be applied using a known process for shrinking a covering or housing against the outer surface of the section requiring protection. U.S. Pat. Nos. 5,080,942 and 4,389,440 describe pre-stretched shrinkable covers used as protective cable closures.
Pre-stretched shrinkable covers, also known as cold-shrink covers or tubes or prestretched tubes (PST), were developed to overcome some of the disadvantages of heat shrink products. Heat-shrink products, while providing effective sealing and protection, approach a condition requiring material flow during recovery of the product to conform to the contours of a cable or cable splice surface. During recovery, a heat shrink cover changes its shape and cannot retain molded features that might be useful during the lifetime of the protected cable section. For example, a heat shrink cover preferably seats snugly around the cable section providing little protection against fatigue during repeated flexing of a splice junction. As a result, the intersection of a main cable and a branch wire represents a point of weakness, which could rupture under stress. The same is true for conventional cold-shrink covers designed without consideration of molded features for stress relief. Consequently, there is a need for sealed cable closures having less susceptibility to rupture under stress. Such closures would extend the duration of protection of cable splices or worn sections of cable as well as being resistant to damage by rough handling during the process of installation.
The present invention provides a protective, sealing, preferably elastomeric cable transition cover including stress-relief for application to wiring harnesses and the like. A cable transition cover according to the present invention accommodates repeated flexing and related distortion during manufacture, installation and subsequent use of wiring structures, which include transition sections produced by diverting wires from a multi-wire cable into connecting branches required by the wiring structure design.
Incorporation of stress relief, into a cable transition cover, allows an increased amount of stretching to place the elastomeric cable covers in a pre-stretched condition thereby facilitating wire insertion. Retention of cable covers in a stretched condition is possible with collapsible, disposable cores that are commonly used in pre-stretched tubing (PST) products, also known as cold shrink products, that find use in electrical cabling applications. Application of stress relief to cable transition covers facilitates core loading without rupture of the elastomeric cover. Being less susceptible to rupture, cable transition covers according to the present invention offer increased versatility and application of pre-stretched structures to a broader range of applications.
One improvement of incorporating stress relief is the manufacture of cable covers having more complex designs for increasing numbers of branches from a primary cable. This improvement also translates into relatively low profile transition covers sized to pass through smaller dimension through-holes formed in walls or bulkheads through which a cable transition section may pass. Size reduction leads to efficient space utilization and design flexibility during integration of wiring structure and vehicle or equipment design.
More particularly the present invention provides a molded article for protecting a transition section of a multi-wire cable. The article comprises a transition cover having an elastomeric skin and further comprising a cable receiving tube, having an open channel therein. The cable receiving tube has intersection with each of a plurality of wire cover sleeves to provide passages opening from the open channel of the cable receiving tube to each of the plurality of wire cover sleeves for insertion of at least one wire of the multi-wire cable therein. A stress relief pocket formed in the elastomeric skin, adjacent to at least a portion of each intersection, extends towards the open channel and includes at least one crease to accommodate expansion of the stress relief pocket from a partially folded condition to reduce the concentration of stress at an intersection during movement of the transition cover from a relaxed condition to a stretched condition.
Definitions
The term xe2x80x9ccable transition coverxe2x80x9d refers to an article applied around a section of cable to protect an underlying cable splice or worn section of cable jacket. A cable transition cover, supplied preferably in a pre-stretched condition, may be installed by shrinking it around the cable upon removal of one or more support cores commonly used in PST products. Cable transition covers according to the present invention include a cable receiving tube attached to one or more wire cover sleeves used to accommodate branch wires or fibers divided out from multiple signal or power carriers included in the main cable.
As used herein the term xe2x80x9cwire cover sleevexe2x80x9d refers to that portion of a cable transition cover that contains and seals a branch wire or fiber extending from the main cable.
An xe2x80x9celastomeric skinxe2x80x9d according to the present invention is the layer of elastomeric, recoverable material used to form a cable transition cover.
Terms including xe2x80x9cstress relief pocketxe2x80x9d or xe2x80x9cfoldxe2x80x9d or xe2x80x9cdishxe2x80x9d or xe2x80x9ccupxe2x80x9d or similar terms may be used interchangeably herein to describe the portion of a cable transition cover according to the present invention that provides relief from stress associated with repeated flexure or severe bending of one or more wire cover sleeves relative to a cable receiving tube. A stress relief pocket may include one or more creases or partial folds, which open to relieve applied stress. Such creases or folds are generally difficult to incorporate into molded elastomeric structures.
Terms such as xe2x80x9cprotectingxe2x80x9d and xe2x80x9cprotectivexe2x80x9d and the like, as applied to cable transition covers, refer to the ability of such covers to seal out moisture and contaminants from the vicinity of signal carrying wires and optical fibers.
A xe2x80x9ctransition sectionxe2x80x9d is that portion of a cable containing a splice or one or more branched signal carriers that require protection following cable modification.
The term xe2x80x9cmulti-wire cablexe2x80x9d is descriptive of an electrical or communications cable that contains a plurality of signal or power carriers, some of which may be separated to produce branched wiring structures.
The term xe2x80x9cstressxe2x80x9d refers to mechanical stress produced by flexure or similar displacement of an article described herein.